Embodiments of the invention relate to a laminate structure for use in a variety of packaging applications, and more particularly, to a laminate structure in which a primer composition is applied to a first polymeric substrate which is subsequently printed with a liquid ink or toner and then laminated to a second polymeric substrate.
Polymeric films such as biaxially oriented polypropylene, biaxially oriented polyethylene terephthalate, or polyester films have been widely used in packaging materials for food, liquids, and toiletries. For such packaging applications, a first polymeric film is often laminated to another polymeric film which may be the same or different from the first polymeric film.
Such films are also often printed with the use of high-speed digital printing machines utilizing liquid or dry toners or inks in electrophotographic systems. In such systems, toner images are formed on a photosensitive drum and then electrically transferred onto an intermediate transfer blanket or belt for printing onto a polymeric film sheet or web. Printers using such toners or inks are commercially available from Hewlett-Packard Company under the trade name HP Indigo. However, as liquid toners do not always transfer well and/or adhere well to polymeric film substrates which are printed using such presses, the substrates are typically coated with a primer to enhance the adhesion of liquid toners thereto.
A number of primers have been developed for use on polymeric film substrates which render the surface of the films more receptive to toners and inks. Typical primers currently in use have been developed based on ethylene-acrylic acid copolymers. One such primer is described in commonly-assigned U.S. Pat. No. 7,470,736.
However, the development of newer, high speed digital presses has presented new challenges to the use of primers with regard to liquid toner and/or ink transfer and adhesion to the polymer substrates. For example, the more recently developed HP Indigo 6000 series of digital presses offer digital printing at about twice the speed of previous Indigo presses. In addition, the HP 20000 digital press is capable of printing a 30-inch (76.2 cm) wide film and the HP 30000 digital press is capable of printing at a 29.5 inch (75.0 cm) width on a variety of substrate types.
Due to the specifications of the liquid toners used in such presses, conventional primers do not provide sufficient toner adhesion to the underlying polymeric substrate. As a result, substrates coated with conventional primers may experience undesirable toner transfer to and adhesion to the substrate as well as resulting in unacceptably low lamination bond strength when the printed film is laminated to another substrate.
Accordingly, there is a need in the art for a primer which provides good toner and/or ink adhesion to polymeric substrates and which provides improved bond strength when used between printed and laminated polymeric substrates.